Cellulose, a polysaccharide formed from glucose via β(1, 4) glycoside linkages by natural processes (Applied Fiber Science, F. Happey, Ed., Chapter 8, E. Atkins, Academic Press, New York, 1979), has achieved commercial prominence as a fiber as a consequence of the many useful products derived therefrom. In particular, cotton, a highly pure form of naturally occurring cellulose, is well-known for its beneficial attributes in textile applications.
Cellulose exhibits sufficient chain extension and backbone rigidity in solution to form liquid crystalline solutions (U.S. Pat. No. 4,501,886). However, sufficient polysaccharide chain extension has hitherto been achieved primarily in β(1, 4) linked polysaccharides. Any significant deviation from that backbone geometry in the glucan polysaccharide family lowers the molecular aspect ratio below that required for the formation of an ordered lyotropic phase. Additionally, it is well-known that important commercial cellulosic fibers such as cotton and rayon increasingly present sustainability issues with respect to land use and environmental imprint.
It is therefore highly desirable to discover other glucose-based polysaccharides with utility in films, fibers and resins largely because of the current emphasis on producing low cost, structural materials from renewable resources. In addition such polymers offer materials that are environmentally benign throughout their entire life cycle.
Poly (α1, 3 glucan), a glucan polymer characterized by having α(1, 3) glycoside linkages, has been isolated by contacting an aqueous solution of sucrose with a glucosyltransferase (gtfJ) enzyme isolated from Streptococcus salivarius (Simpson et al., Microbiology, 141: 1451-1460, 1995). Glucan refers to a polysaccharide composed of D-glucose monomers linked by glycosidic bonds. Films prepared from poly (α1, 3 glucan) tolerated temperatures up to 150° C. and provided an advantage over polymers obtained from β(1, 4) linked polysaccharides (Ogawa et al., Fiber Differentiation Methods, 47: 353-362, 1980).
U.S. Pat. No. 7,000,000 disclosed preparation of a polysaccharide fiber comprising hexose units, wherein at least 50% of the hexose units within the polymer were linked via α(1, 3) glycoside linkages using the glucosyltransferase enzyme gtfJ of Streptococcus salivarius. The disclosed polymer formed a liquid crystalline solution when it was dissolved above a critical concentration in a solvent or in a mixture comprising a solvent. From this solution continuous, strong, cotton-like fibers, highly suitable for use in textiles, were spun and used either in a derivatized form or as a non-derivatized (regenerated) form. The poly (α1, 3 glucan) in U.S. Pat. No. 7,000,000 was made in a batch process wherein the poly (α1, 3 glucan) titers were typically less than 25 grams of poly (α1, 3 glucan) per liter of the reactor volume.
It can be desirable to develop processes to increase the titer of the poly (α1, 3 glucan) formed by the enzymatic reaction.